Blood pump

ABSTRACT

An intravascular blood pump ( 1 ) comprises a pump casing ( 2 ) having a blood flow inlet ( 21 ) and a blood flow outlet ( 22 ), and an impeller ( 3 ) arranged in said pump casing ( 2 ) so as to be rotatable about an axis of rotation, wherein the impeller ( 3 ) has blades ( 31 ) sized and shaped for conveying blood from the blood flow inlet ( 21 ) to the blood flow outlet ( 22 ). The blood pump ( 1 ) further comprises a drive unit ( 104 ) for rotating the impeller ( 3 ), the drive unit ( 104 ) comprising a plurality of posts ( 140 ) arranged about the axis of rotation ( 10 ). Coil windings ( 47 ) around the posts are sequentially controllable so as to create a rotating magnetic field. The shaft portion ( 141 ) of each of the posts ( 140 ) comprises a soft magnetic material which is discontinuous in cross-section transverse to the longitudinal axis of the respective post ( 140 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/648,337, filed Mar. 18, 2020, now allowed, which is a United StatesNational Stage Filing under 35 U.S.C. § 371 of International ApplicationNo. PCT/EP2018/074929, filed Sep. 14, 2018, which claims priority toEuropean Patent Application No. 17191940.0, filed Sep. 19, 2017. Thecontents of each of the foregoing applications are hereby incorporatedby reference in their entirety. International Application No.PCT/EP2018/074929 was published under PCT Article 21(2) in English.

BACKGROUND OF THE INVENTION

This invention relates to a blood pump, in particular an intravascularblood pump for percutaneous insertion into a patient's blood vessel, tosupport a blood flow in a patient's blood vessel. The blood pump has animproved drive unit which allows for reduction of the outer diameter ofthe blood pump.

Blood pumps of different types are known, such as axial blood pumps,centrifugal (i.e. radial) blood pumps or mixed-type blood pumps, wherethe blood flow is caused by both axial and radial forces. Intravascularblood pumps are inserted into a patient's vessel such as the aorta bymeans of a catheter. A blood pump typically comprises a pump casinghaving a blood flow inlet and a blood flow outlet connected by apassage. In order to cause a blood flow along the passage from the bloodflow inlet to the blood flow outlet, an impeller or rotor is rotatablysupported within the pump casing, with the impeller being provided withblades for conveying blood.

Blood pumps are typically driven by a drive unit, which can be anelectric motor. For instance, US 2011/0238172 A1 disclosesextracorporeal blood pumps having an impeller which may be magneticallycoupled to an electric motor. The impeller comprises magnets which aredisposed adjacent to magnets in the electric motor. Due to attractingforces between the magnets in the impeller and in the motor, rotation ofthe motor is transmitted to the impeller. In order to reduce the numberof rotating parts, it is also known from US 2011/0238172 A1 to utilize arotating magnetic field, with the drive unit having a plurality ofstatic posts arranged about the axis of rotation, and each post carryinga wire coil winding and acting as a magnetic core. A control unitsequentially supplies a voltage to the coil windings to create therotating magnetic field. In order to provide a sufficiently strongmagnetic coupling, the magnetic forces have to be high enough, which canbe achieved by a sufficiently high current supplied to the drive unit orby providing large magnets, which, however, leads to a large overalldiameter of the blood pump. However, high energy consumption and heatgeneration may occur in such drive units.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a bloodpump, preferably an intravascular blood pump or transvalvular bloodpump, having a magnetic coupling between the drive unit and theimpeller, wherein the blood pump has a compact design, in particular asufficiently small outer diameter to allow the blood pump to be insertedtransvascularly, transvenously, transarterially or transvalvularly. Itis further an object of the present invention to reduce heat and energyconsumption of the blood pump, which is particularly useful forlong-term applications in which the blood pump can be battery-powered toprovide mobility for the patient.

This object is achieved according to the present invention by a bloodpump having the features of independent claim 1. Preferred embodimentsand further developments of the invention are specified in the claimsdependent thereon.

According to the invention, the blood pump, which preferably is anintravascular blood pump and may be an axial blood pump or a diagonalblood pump, which pumps partly axially and partly radially, (thediameter of pure centrifugal blood pumps is usually too large forintravascular applications), comprises a drive unit for rotating theimpeller. The drive unit comprises a plurality of posts, such as atleast two, at least three, at least four, at least five or preferablysix posts, that are arranged about the axis of rotation. Higher numbersof posts, such as eight, ten or twelve, may be possible. The number ofposts is preferably even for a balanced control of the impeller, but itmay also be odd, such as three or five. Each of the posts includes ashaft portion and a head portion, with the head portion pointing towardsthe impeller. In order to create a rotating magnetic field, a coilwinding is disposed about the shaft portion of each of the posts, withthe coil windings being sequentially controllable so as to create therotating magnetic field. The impeller comprises at least one magnet,which is arranged to magnetically couple the impeller to the drive unit,i.e. to interact with the rotating magnetic field so as to causerotation of the impeller.

A drive unit that creates a rotating electromagnetic field allows forsimplification of the mechanics of the blood pump by reducing the numberof moving parts compared to a common electric motor. This also reduceswear, because no contact bearing for an electric motor is necessary. Themagnetic coupling between the drive unit and the impeller not onlycauses rotation of the impeller but also permits correct alignment ofthe impeller.

Each of the posts has a longitudinal axis, and the shaft portion of eachof the posts extends along the longitudinal axis of the respective post.Preferably, the longitudinal axis of each post is parallel to the axisof rotation. The shaft portion of each of the posts comprises a softmagnetic material which is discontinuous in cross-section transverse,preferably perpendicular, to the longitudinal axis of the respectivepost. In other words, the soft magnetic material of the posts isdiscontinuous in cross-section transverse, preferably perpendicular, toa direction of magnetic flux caused by the respective coil winding inthe shaft portion. By dividing or interrupting the soft magneticmaterial in cross section, eddy currents in the shaft portions of theposts can be reduced or avoided, such that heat generation and energyconsumption can be reduced. Reducing energy consumption is particularlyuseful for long term applications of the blood pump, in which it isdesirable that the blood pump is battery-powered to provide mobility forthe patient. Also in long term applications, the blood pump may beoperated without purge, which is only possible if heat generation islow.

“Discontinuous” in the sense of the present document means that the softmagnetic material as seen in any cross-section transverse to thelongitudinal axis is interrupted, separated, intersected or the like bymeans of insulating material or other materials or gaps in order to formstrictly separated areas of soft magnetic material or areas that areinterrupted but connected at a different location.

Providing a discontinuous soft magnetic material in cross-sectionalplanes transverse to the direction of the magnetic flux reduces eddycurrents and thus heat generation and energy consumption as explainedabove. In order not to substantially weaken the magnetic field comparedto a continuous or full body (i.e. solid) soft magnetic material, thetotal amount of soft magnetic material is to be maximized whileminimizing the continuous areas of soft magnetic material. This can beachieved for example by providing the soft magnetic material in the formof a plurality of sheets of soft magnetic material, such as electricsteel. In particular, the sheets may form a stack of sheets. The sheetsare preferably electrically insulated from each other, e.g. by providingadhesive, lacquer, baking enamel or the like between adjacent ones ofthe sheets. Such arrangement can be denoted as “slotted”. Compared to afull body soft magnetic material, the amount of soft magnetic materialis recued only little and the amount of insulating material is keptsmall, such that the magnetic field caused by a slotted post issubstantially the same as the magnetic field caused by a solid post. Inother words, while heat generation and energy consumption can be reducedsignificantly, the loss in magnetic field caused by the insulatingmaterial is insignificant.

The sheets preferably extend substantially parallel to the longitudinalaxis of the respective post. In other words, the sheets may extendsubstantially parallel to the direction of the magnetic flux, such thatthe shaft portions are discontinuous in cross-section transverse orperpendicular to the direction of the magnetic flux. It will beappreciated that the sheets may extend at an angle relative to thelongitudinal axis of the respective post as long as the soft magneticmaterial is discontinuous in cross-section transverse to thelongitudinal axis. The sheets preferably have a thickness in the rangeof about 25 μm to about 350 μm, more preferably about 50 μm to about 200μm, for instance 100 μm.

It is generally known to provide slotted soft magnetic material, such aselectrical steel, in electric motors to avoid or reduce eddy currents.However, this technology has been applied for large devices in which thesheets usually have a thickness in the range of about 500 μm or higher.In small applications, such as the blood pump of the present invention,in which one of the posts, more specifically the respective shaftportion, usually has a diameter in said order of magnitude, and in whichthe power input is relatively low (e.g. up to 20 watts (W)), eddycurrents and the associated problems were not expected. Surprisingly,despite the small diameter of the shaft portions, eddy currents and thusheat generation and energy consumption can be reduced by providing aslotted shaft portion. This is advantageous for operation of the bloodpump, which may be operated at a high speed of up to 50,000 rpm(revolutions per minute).

It will be appreciated that other arrangements than the aforementionedslotted arrangement to provide a discontinuous soft magnetic material inthe shaft portions of the posts may be possible. For instance, insteadof a plurality of sheets, a plurality of wires, fibers, posts or otherelongate elements can be provided to form each of the posts of the driveunit. The wires or the like may be provided in the form of a bundle withthe wires being electrically insulated from each other, e.g. by means ofa coating surrounding each wire or an insulating matrix in which thewires are embedded, and may have various cross-sectional shapes, such ascircular, round, rectangular, square, polygonal etc. Likewise, particlesof a soft magnetic material, wire wool or other sponge-like or porousstructures of soft magnetic material can be provided, in which the spacebetween the areas of soft magnetic material comprises an electricallyinsulating material, such as an adhesive, lacquer, polymer matrix or thelike. A porous and, thus, discontinuous structure of soft magneticmaterial may also be formed by a sintered material or pressed material.In such structure, an additional insulating material may be omittedbecause insulating layers may be formed automatically by oxide layersresulting from oxidation of the soft magnetic material by exposure toair.

While the sheets or other structures of soft magnetic material may beformed uniformly, i.e. the sheets within one of the posts or all postsmay have the same thickness or wires may have the same diameter, anon-uniform arrangement can be provided. For instance, the sheets mayhave a varying thickness or the wires may have a varying diameter. Morespecifically, in particular with regards to a stack of sheets, one ormore central sheets may have a larger thickness, while adjacent sheetstowards the ends of the stack may have a smaller thickness, i.e. thethickness of the sheets decreases from the center towards the ends ofthe stack, i.e. towards the outermost sheets of the stack. Similarly,one or more central wires in a bundle of wires may have a largerdiameter, while wires at the edge of the shaft portion of the post mayhave a smaller diameter, i.e. the diameter of the wires may decreasefrom the center towards the edges of the bundle, i.e. towards theoutermost wires of the bundle. Providing a larger continuous area ofsoft magnetic material in the center of the shaft portion with respectto a cross-section transverse to its longitudinal axis, i.e. relativelythick sheets or wires in the center, may be advantageous because thismay enhance the magnetic flux through the center along the longitudinalaxis of each post, and eddy currents in the center are less relevantthan eddy currents at the sides of the posts. In other words, sucharrangement may be advantageous because eddy currents in the sideregions of the shaft portions are more critical and can be reduced bythin sheets or wires in the side regions.

In one embodiment, the head portion of each of the posts may comprise asoft magnetic material that is discontinuous in cross-sectionperpendicular to the longitudinal axis of the respective post.Substantially all features and explanations as set forth above withrespect to the discontinuous material of the shaft portions are validfor the head portions. For instance, like the shaft portions, the headportions may be slotted, and the sheets of the head portions arepreferably electrically insulated from each other. Since the magneticflux in the head portions is substantially parallel to the axis ofrotation or the longitudinal axis of the respective post, especially ifthe head portions do not have inclined surfaces as will be describedbelow, the soft magnetic material of the head portions may be providedin the form of a plurality of sheets that extend parallel to thelongitudinal axis of the respective post, or to the axis or rotation. Inother words, the sheets in the head portions may extend substantially inthe same direction as the sheets of the shaft portions. As explained inthe aforementioned, eddy currents and thereby heat generation and powerconsumption can be reduced. However, since eddy currents in the headportions are usually low, the effect of a discontinuous materialcompared to a solid material is not as significant as in the shaftportions. Thus, the head portions may be alternatively formed ofcontinuous, i.e. solid, soft magnetic material.

The drive unit may further comprise a back plate which may engage endsof the shaft portions of the plurality of posts that are opposite to thehead portions. In one embodiment, the back plate may comprise aplurality of apertures arranged about the axis of rotation for receivingsaid ends of the shaft portions, preferably at a regular angulardistance. However, it will be appreciated that the post can be attached,connected or secured to the back plate by other means, eitherpermanently or releasably. The back plate particularly serves forclosing the magnetic flux circuit to facilitate and increase themagnetic flux generation and improve the coupling capability. Since themagnetic flux is increased by the back plate, the overall diameter ofthe blood pump can be reduced, which is particularly advantageous forintravascular blood pumps. The arrangement including the posts with theback plate further allows for high frequencies of the blood pump, i.e.the blood pump can operate at a high speed, e.g. up to about 50,000 rpm.In addition, as the back plate engages the posts, the back plateprovides structural stability for the post assembly.

Like the shaft portions and possibly the head portions of the posts, theback plate may comprise a discontinuous soft magnetic material. Sincethe magnetic flux in the back plate is substantially transverse orperpendicular to the axis of rotation, the soft magnetic material of theback plate is preferably discontinuous in cross-section parallel to theaxis of rotation. Apart from that, substantially all features andexplanations mentioned above with respect to the discontinuous materialof the shaft portions are valid also for the back plate. For instance,like the shaft portions, the back plate may be slotted, i.e. may beformed of a plurality of stacked sheets, and the sheets of the backplate are preferably electrically insulated from each other. The sheetsof the back plate may extend substantially perpendicularly to the sheetsof the shaft portions and substantially parallel to the sheets of thehead portions. As explained in the aforementioned, eddy currents andthereby heat generation and power consumption can be reduced. However,the back plate may be alternatively formed of continuous, i.e. solid,soft magnetic material.

The back plate, like the posts, is preferably made of a soft magneticmaterial, such as electrical steel (magnetic steel) or other materialsuitable for closing the magnetic flux circuit, preferably cobalt steel.The diameter of the back plate may be about 3 mm to 9 mm, such as 5 mmor 6 mm to 7 mm. The thickness of the back plate may be about 0.5 mm toabout 2.5 mm, such as 1.5 mm. The outer diameter of the blood pump maybe from about 4 mm to about 10 mm, preferably about 6 mm. The outerdiameter of the arrangement of the plurality of posts, in particular thelargest outer diameter of the arrangement of the plurality of postswhich is measured at the head portions of the posts may be about 3 mm to8 mm, such as 4 mm to 6 mm, preferably 5 mm.

As stated above, the posts are made of a soft magnetic material such aselectrical steel (magnetic steel). The posts and the back plates may bemade of the same material. Preferably, the drive unit, including theposts and the back plate, is made of cobalt steel. The use of the cobaltsteel contributes to reducing the pump size, in particular the diameter.With the highest magnetic permeability and highest magnetic saturationflux density among all magnetic steels, cobalt steel produces the mostmagnetic flux for the same amount of material used.

The dimensions of the posts, in particular length and cross-sectionalarea, may vary and depend on various factors. In contrast to thedimensions of the blood pump, e.g. the outer diameter, which depend onthe application of the blood pump, the dimensions of the posts aredetermined by electromagnetic properties, which are adjusted to achievea desired performance of the drive unit. One of the factors is the fluxdensity to be achieved through the smallest cross-sectional area of theposts. The smaller the cross-sectional area, the higher is the necessarycurrent to achieve the desired magnetic flux. A higher current, however,generates more heat in the wire of the coil due to electricalresistance. That means, although “thin” posts are preferred to reducethe overall size, this would require high current and, thus, result inundesired heat. The heat generated in the wire also depends on thelength and diameter of the wire used for the coil windings. A short wirelength and a large wire diameter are preferred in order to minimize thewinding loss (referred to as “copper loss” or “copper power loss” ifcopper wires are used, which is usually the case). In other words, ifthe wire diameter is small, more heat is generated compared to a thickerwire at the same current, a preferred wire diameter being e.g. 0.05 mmto 0.2 mm, such as 0.1 mm. Further factors influencing the postdimensions and the performance of the drive unit are the number ofwindings of the coil and the outer diameter of the windings, i.e. thepost including the windings. A large number of windings may be arrangedin more than one layer around each post, for instance, two or threelayers may be provided. However, the higher the number of layers, themore heat will be generated due to the increased length of the wire inthe outer layers having a larger winding diameter. The increased lengthof the wire may generate more heat due to the higher resistance of along wire compared to a shorter one. Thus, a single layer of windingswith a small winding diameter would be preferred.

A typical number of windings, which in turn depends on the length of thepost, may be about 50 to about 150, e.g. 56 or 132. Independent of thenumber of windings, the coil windings are made of an electricallyconductive material, in particular metal, such as copper or silver.Silver may be preferred to copper because silver has an electricalresistance which is about 5% less than the electrical resistance ofcopper.

In one embodiment, the impeller may also comprise a yoke or back platethat is attached to the at least one magnet of the impeller, preferablyat a side of the impeller facing away from the drive unit, e.g. betweenthe magnet and blades of the impeller. Like the back plate that isattached to the ends of the shafts of the posts, the yoke or back plateof the impeller serves for closing the magnetic flux circuit to increasethe magnetic flux generation and enhance the coupling capability. It maybe made of magnetic steel, preferably cobalt steel.

In order to increase the density of the magnetic coupling between thedrive unit and the magnets of the impeller, it may be advantageous toactivate several posts simultaneously, where “activate” means to supplyelectric power to the respective coil winding in order to create arespective pole magnet. For example, more than half of the posts may beactivated at the same time, such as four of six posts, depending on thenumber of posts and number of magnets in the impeller. Preferably, thearrangement of activated and inactivated posts is rotationallysymmetrical and the posts are controlled preferably in pairs ofdiametrically opposing posts.

It may be further advantageous for the efficiency and performance of thedrive unit if the posts are magnetically insulated against each other.Thus, a magnetically insulating material may be disposed between thehead portions of adjacent posts so as to separate the posts from eachother and keep the respective magnetic field within the respective post.The magnetically insulating material may be a magnetic material, themagnetic field of which keeps the electromagnetic field caused by thecoil windings within the respective post. At least, an air gap or otherinsulating, i.e. electrically non-conductive, material may be providedbetween the head portions of the posts to avoid a short-circuit betweenthe posts.

In one embodiment, the head portion of at least one of the posts,preferably of each of the posts, has a top surface that is inclined atan angle relative to a plane perpendicular to the axis of rotation. Adistance between the axis of rotation and a center in a radial directionof said inclined surface may be less than or equal to a distance betweenthe axis of rotation and a center in a radial direction of across-sectional area of the shaft portion of the respective post. Thecenter in a radial direction of a surface or area is the center betweena radially innermost point and a radially outermost point of the surfaceor area. In other words, the inclined top surface of the head portion,which is the surface facing the impeller, may extend obliquely or may beinclined at an angle relative to the axis of rotation, and half or moreof the inclined surface may be located radially inwards relative to thecenter of the shaft portion. This enables the outer diameter of thedrive unit and, thus, of the blood pump, to be kept at a minimum that isnecessary for magnetically coupling the drive unit to the impeller. Thisreduced diameter design is particularly advantageous for intravascularblood pumps that are located within a patient's blood vessel during pumpoperation and can be deployed by means of a catheter. In addition, theinclined coupling surface provides for radial centering of the impeller.The aforementioned angle is preferably 45°, but may be between about 0°and about 90°, preferably between about 30° and about 60°, morepreferably between about 40° to about 50°, with respect to a planeperpendicular to the axis of rotation. The inclined surfaces of theposts preferably face radially outwards, i.e. they form a convex shape.Alternatively, the inclined surfaces may face radially inwards to form aconcave shape.

In another embodiment, the top surfaces of the head portions of theposts may be perpendicular to the axis of rotation. In other words, thetop surfaces of the head portions may have no inclination compared tothe aforementioned embodiment, such that the head portions do not form aconical shape but form a flat plane. Accordingly, the magnets in thisembodiment are not inclined but form a flat plane that is parallel tothe plane formed by the top surfaces of the head portions.

All of the posts preferably are identical such that the drive unit issymmetrical with respect to the axis of rotation. It will beappreciated, however, that the posts do not have to be exactly identicalas long as they are compatible for forming the drive unit according tothe invention. However, it is preferable for shaft portions to have thesame length and the inclined surfaces of the head portions to have thesame angle of inclination. Different posts may be irregularly orregularly arranged to form the drive unit, such as in an alternatingmanner.

The top surface of the head portion, preferably of each of the headportions, whether inclined or not as explained above, may be radiallyaligned with or be located radially inwards or outwards with respect toa radially outermost surface of the coil winding of the respective post.The top surface preferably extends radially inwards beyond therespective shaft portion towards the axis of rotation so as to maximizethe surface area of the magnetic bearing, while minimizing the outerdiameter of the drive unit. For instance, in an axial projection, i.e.as seen in a top view in an axial direction, the top surface of the headportion may be located within the coil winding or may be at leastaligned with the shaft or coil winding in an axial direction. In anotherembodiment, the head portion may extend beyond the outer circumferenceof the coil winding in a radial and/or circumferential direction. Thehead portion may have a larger cross-sectional dimension than therespective shaft portion in a plane perpendicular to the axis ofrotation, with the respective coil winding preferably not extendingbeyond the head portion at least in a radial direction. In other words,the head portion may form a shoulder, which can act as an axial stop forthe coil winding as well as a radial limitation.

In case the top surfaces of the head portions are oblique or inclined,at least one of the head portions, preferably all head portions, may besubstantially triangular or trapezoidal in cross-section along a planeincluding the axis of rotation. In the assembled state, the oblique orinclined surfaces of the head portions may together form a conicalsurface or substantially conical surface, e.g. a surface having facetsbut forming approximately a conical surface. Generally, the shape of theformed surface can be convex. Illustratively speaking, the head portionsmay be put together like pie slices to form a circular arrangementhaving a conical top surface. The at least one magnet of the impellermay have or may form a conical or substantially conical recesssubstantially corresponding in size and shape to the conical surfaceformed by the head portions of the posts. Generally, the magnet may forma concave surface facing the convex surface formed by the posts toimprove the magnetic coupling. In another embodiment, the arrangement ofconcave and convex surfaces may be vice versa, i.e. the head portions ofthe posts may form a conical recess while the magnet forms a convexconical surface.

The respective convex and concave surfaces of the drive unit and theimpeller respectively may form a gap such that the distance between thesurfaces is constant. Preferably, however, the gap distance is notconstant but is chosen such that the cross-sectional area of the gap,viewed in a circumferential direction, is constant in a radialdirection. In the latter case the distance between the surfacesincreases towards the axis of rotation. Combinations may also beenvisioned. The shape and dimension of the gap between the impeller andthe drive unit may contribute to hydrodynamic bearing capabilities.Similarly, such gap is provided if the top surfaces of the head portionsare not inclined.

The magnet of the impeller may be formed as a single piece having theconical or substantially conical recess that corresponds to the shape ofthe head portions of the posts, including a gap with varying distance asexplained above. It will be appreciated, however, that there may beprovided a plurality of magnets, such as two or more, e.g. four,preferably six magnets, or even eight, ten or twelve magnets, that arearranged in the impeller about the axis of rotation and form the conicalrecess. Providing a plurality of magnets, preferably an even number,more preferably a number corresponding to the number of posts, isadvantageous because the magnets can be arranged with alternatingnorth/south orientations of the magnetic field without dead zones. Ifthe magnet is provided as a single piece, dead zones may be created atthe transitions between differently oriented magnetic fields. It will beappreciated that the aforementioned structure may also apply if themagnet or magnets and the top surfaces of the head portions are notinclined but lie in planes perpendicular to the axis of rotation.

If the impeller includes a plurality of magnets, the magnets may bearranged with substantially no gaps between the individual magnets inorder to increase the amount of magnetic material. However, it has beenfound that the efficiency of the magnetic coupling does not decrease ifthe magnets are separated by gaps, in particular radially extendinggaps. This is because of the characteristics of the magnetic field andthe gap between the drive unit and the impeller. If the magnets in theimpeller are close to each other, the innermost magnetic field lines,which extend in an arch from one magnet (north) to an adjacent magnet(south), do not extend beyond the gap between the drive unit and theimpeller and, thus, do not reach the drive unit, i.e. they do notcontribute to the drive of the impeller. Therefore, there is no loss inefficiency if a gap is provided between the magnets in the impeller. Thesize of gap between the magnets in the impeller that can be providedwithout loss of efficiency of the drive is dependent on the size of thegap between the impeller and the drive unit as a skilled person cancalculate. The gaps between the impeller magnets can then be used e.g.as wash out channels.

Generally speaking and regardless of whether the head portions form aconical surface, the magnet of the impeller may have a surface thatfaces the head portions of the posts and is inclined at an anglesubstantially corresponding to the angle of the inclined surfaces of thehead portions. For instance, the arrangement may be the converse of theaforementioned arrangement, that is to say, the head portions of theposts may form a concave surface, such as a conical recess, and themagnet of the impeller may form a convex surface, such as a conicalsurface. This also applies if the surfaces are not inclined, i.e. if theaforementioned angle is 90 degrees with respect to the axis of rotation.

Regardless of the inclination of the respective surfaces, the magnet ormagnets of the impeller may be radially aligned with the head portionsof the posts. However, in some embodiments, the magnet or magnets of theimpeller may be radially offset with respect to the head portions of theposts, such as radially inwards or radially outwards. This radial offsetmay improve stabilizing and radial centering of the impeller because themagnetic forces between the impeller and the drive unit have a radialcomponent, whereas the magnetic forces are directed merely substantiallyaxially if the magnets are radially aligned with the head portion of theposts.

In one embodiment, the impeller may extend at least partially about thedrive unit, in particular the head portions of the posts. In otherwords, the impeller may have an extension that overlaps the drive unitin a circumferential direction. That means the magnetic coupling takesplace not only in the region of the inclined surfaces of the headportions of the posts but also on radially outer side surfaces thereof.The impeller may have an increased diameter, in particular a largerdiameter than the drive unit, such that the impeller can extend aboutthe area of the head portions of the posts. The impeller may, thus, havea recess that has a conical portion as described above and a cylindricalportion. The magnetic coupling can be improved by this design of theimpeller because the impeller and the drive unit are coupled in a radialdirection as well, where the magnetic field lines extend in a radialdirection. In this area, a high torque can be created to drive theimpeller due to the largest diameter.

In one embodiment, the intravascular blood pump may further comprise ahousing surrounding the drive unit, with the housing preferablycorresponding in size and shape to an outer contour of the plurality ofposts. In particular, the housing may have a conical axial end surfacecorresponding to the shape of the surface formed by the inclinedsurfaces of the posts' head portions. The opposite end may be open andmay engage the back plate to close the housing. The housing serves as aprotection for the post assembly, particularly as a protection againstblood contact, which is particularly useful for the coil windings.Preferably, the housing is disposed inside the pump casing. Regardlessof the presence of such housing, the drive unit preferably is arrangedinside the pump casing. The housing is preferably made of a non-magneticand non-conductive (i.e. electrically insulating) material and providesgood heat transfer. The material of the housing may be e.g. aluminum.

The coil windings may be embedded in a thermally conductive matrix,which is electrically non-conductive (i.e. electrically insulting). Thematrix protects the coil windings and transfers heat produced by thecoil windings. The material of the thermally conductive matrix maybe aplastics material with additives in order to increase the thermallyconductive characteristics. For instance, the matrix may comprise anepoxy resin with aluminum additives. The matrix may be formed by moldingthe material around and between the coil windings and subsequentlycuring the material.

The drive unit may have a central opening that extends along the axis ofrotation. The central opening may be formed by the head portions of theposts and may be configured for receiving an elongate pin or shaft, withan axial end surface of the pin being sized and dimensioned to form abearing surface for the impeller. This arrangement allows for a compactdesign of the blood pump because the space between the posts is used forthe pin. The other end of the pin may be supported by the pump casing.The central opening may also be provided for insertion of a guide wireor the like or may form a fluid path. In another embodiment in which theblood pump does not have a shaft that extends all the way through thedrive unit, such central opening can be omitted.

In order to enhance a wash-out flow through the gap between the impellerand the drive unit, a secondary set of blades may be provided in theimpeller. In particular, secondary blades may be provided on the side ofthe magnet or magnets that faces the drive unit, i.e. in the gap betweenthe impeller and the drive unit. The wash-out flow may additionally oralternatively be increased by channels that are recessed in the surfaceof the magnet that faces the drive unit. The channels may extend e.g.radially or helically.

In one embodiment, one or more hydrodynamic bearings may be provided tosupport the impeller. For instance, the aforementioned secondary bladesand the channels may form a hydrodynamic bearing or at least supporthydrodynamic bearing capabilities as mentioned above with respect to thesize and shape of the gap between the impeller and the drive unit.Conversely, the surface of the drive unit that faces the impeller, i.e.in particular the end surface of the housing that encloses the driveunit, may be adapted to form a hydrodynamic bearing. The hydrodynamicbearing may be axial or radial or both axial and radial. In particularbecause of the conical shape of the interface between the impeller andthe drive unit, a hydrodynamic bearing in both radial and axialdirections can be formed. A radial hydrodynamic bearing may also beformed between an outer surface of the impeller and an inner surface ofthe pump casing. In particular, a gap may be formed between the impellerand the pump casing, where an amount of blood sufficient for thehydrodynamic bearing flows through the gap and exits the pump casingthrough an additional blood flow outlet. The main blood flow exits thepump casing through the blood flow outlet and does not flow through thegap. Hydrodynamic bearings, which are contactless bearings, may supportthe function of the drive unit by reducing frictional forces.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments, will be better understood when read inconjunction with the appended drawings. For the purpose of illustratingthe present disclosure, reference is made to the drawings. The scope ofthe disclosure is not limited, however, to the specific embodimentsdisclosed in the drawings. In the drawings:

FIG. 1 shows a cross-sectional view of a blood pump according to theinvention.

FIG. 2 a shows an enlarged detail of the blood pump of FIG. 1 .

FIG. 2 b shows the same view as FIG. 2 a according to an alternativeembodiment.

FIG. 3 shows a perspective view of a post of a drive unit.

FIGS. 4 a-4 d show different views of another embodiment of a post.

FIG. 5 shows an arrangement including six posts.

FIG. 6 shows the arrangement of FIG. 5 along with a back plate.

FIG. 7 shows the arrangement of FIG. 6 along with coil windings.

FIG. 8 shows the arrangement of FIG. 7 along with a housing.

FIGS. 9 a-9 c show different views of a back plate.

FIGS. 10 a-10 c show different views of the magnets of the impeller.

FIG. 11 shows another embodiment of a drive unit.

FIG. 12 shows another embodiment of a blood pump.

FIGS. 13 a and 13 b show different views of a drive unit and impellermagnets according to another embodiment.

FIGS. 14 a and 14 b schematically illustrate magnetic field linesbetween magnets of the impeller.

FIG. 15 shows a cross-sectional view of a drive unit and impellermagnets according to another embodiment.

FIG. 16 schematically illustrates an operating mode of the drive unit.

FIG. 17 shows another embodiment of a drive unit.

FIG. 18 shows the back plate of the drive unit of FIG. 17 .

FIG. 19 a shows a side view of a post of the drive unit of FIG. 17 .

FIG. 19 b shows another embodiment of a post.

FIG. 19 c shows a perspective view of still another embodiment of apost.

FIG. 19 d shows a perspective view of yet another embodiment of a post.

FIGS. 20 a and 20 b show the drive unit of FIG. 17 with differentmagnets.

FIGS. 21 a to 21 j show cross-sections through the shaft portions ofposts according to various embodiments.

DETAILED DESCRIPTION

Referring to FIG. 1 , a cross-sectional view of a blood pump 1 isillustrated. FIG. 2 shows an enlarged view of the interior of the bloodpump 1. The blood pump 1 comprises a pump casing 2 with a blood flowinlet 21 and a blood flow outlet 22. The blood pump 1 is designed as anintravascular pump, also called a catheter pump, and is deployed into apatient's blood vessel by means of a catheter 25. The blood flow inlet21 is at the end of a flexible cannula 23 which may be placed through aheart valve, such as the aortic valve, during use. The blood flow outlet22 is located in a side surface of the pump casing 2 and may be placedin a heart vessel, such as the aorta. The blood pump 1 is connected tothe catheter 25, with an electric line 26 extending through the catheter25 for supplying the blood pump 1 with electric power in order to drivethe pump 1 by means of a drive unit 4, as explained in more detailbelow.

If the blood pump 1 is intended to be used in long term applications,i.e. in situations in which the blood pump 1 is implanted into thepatient for several weeks or even months, electric power is preferablysupplied by means of a battery. This allows a patient to be mobilebecause the patient is not connected to a base station by means ofcables. The battery can be carried by the patient and may supplyelectric energy to the blood pump 1, e.g. wirelessly.

The blood is conveyed along a passage 24 connecting the blood flow inlet21 and the blood flow outlet 22 (blood flow indicated by arrows). Animpeller 3 is provided for conveying blood along the passage 24 and ismounted to be rotatable about an axis of rotation 10 within the pumpcasing 2 by means of a first bearing 11 and a second bearing 12. Theaxis of rotation 10 is preferably the longitudinal axis of the impeller3. Both bearings 11, 12 are contact-type bearings in this embodiment. Atleast one of the bearings 11, 12 could be a non-contact-type bearing,however, such as a magnetic or hydrodynamic bearing. The first bearing11 is a pivot bearing having spherical bearing surfaces that allow forrotational movement as well as pivoting movement to some degree. A pin15 is provided, forming one of the bearing surfaces. The second bearing12 is disposed in a supporting member 13 to stabilize the rotation ofthe impeller 3, the supporting member 13 having at least one opening 14for the blood flow. Blades 31 are provided on the impeller 3 forconveying blood once the impeller 3 rotates. Rotation of the impeller 3is caused by a drive unit 4 magnetically coupled to a magnet 32 at anend portion of the impeller 3. The illustrated blood pump 1 is amixed-type blood pump, with the major direction of flow being axial. Itwill be appreciated that the blood pump 1 could also be a purely axialblood pump, depending on the arrangement of the impeller 3, inparticular the blades 31.

FIG. 2 a illustrates in more detail the interior of the blood pump 1, inparticular the impeller 3 and the drive unit 4. The drive unit 4comprises a plurality of posts 40, such as six posts 40, only two ofwhich are visible in the cross-sectional view of FIG. 2 . The posts 40have a shaft portion 41 and a head portion 42. The head portion 42 isdisposed adjacent to the impeller 3 in order to magnetically couple thedrive unit 4 to the impeller 3. For this purpose, the impeller 3 has amagnet 32, which is formed as a multiple piece magnet in this embodimentas described in more detail with reference to FIGS. 10 a-c . The magnet32 is disposed at the end of the impeller 3 facing the drive unit 4. Theposts 40 are sequentially controlled by a control unit (not shown) inorder to create a rotating magnetic field for driving the blood pump 1.The magnet 32 is arranged to interact with the rotating magnetic fieldso as to cause rotation of the impeller 3 about the axis of rotation 10.Coil windings are arranged about the shaft portions 41 of the posts 40,as described in more detail below with reference to FIG. 7 . The posts40 are arranged parallel to the axis of rotation 10, more specifically,a longitudinal axis of each of the posts 40 is parallel to the axis ofrotation 10.

In order to close the magnetic flux path, a back plate 50 is located atthe end of the shaft portions 41 opposite the head portions 42. Theposts 40 act as a magnetic core and are made of a suitable material, inparticular a soft magnetic material, such as steel or a suitable alloy,in particular cobalt steel. Likewise, the back plate 50 is made of asuitable soft magnetic material, such as cobalt steel. The back plate 50enhances the magnetic flux, which allows for reduction of the overalldiameter of the blood pump 1, which is important for intravascular bloodpumps. For the same purpose, a yoke 37, i.e. an additional back plate,is provided in the impeller 3 at a side of the magnet 32 facing awayfrom the drive unit 4. The yoke 37 in this embodiment has a conicalshape in order to guide the blood flow along the impeller 3. The yoke 37may be made of cobalt steel, too. One or more wash-out channels thatextend towards the central bearing may be formed in the yoke 37 or themagnet 32.

FIG. 2 b illustrates an alternative embodiment which is substantiallysimilar to the embodiment of FIG. 1 and FIG. 2 a with the exception thattop surfaces of the head portions 42 facing the magnet 32 are notinclined but extend in a plane perpendicular to the axis of rotation.Accordingly, the magnet 32 does not have inclined surfaces but forms asubstantially cylindrical shape.

Details of the drive unit 4 are shown in FIGS. 3 to 9 , while FIG. 10illustrates the magnet 32 of the impeller 3. Referring to FIG. 3 , oneof the posts 40 is shown in a perspective view. In this embodiment, allof the posts 40 in the assembly (i.e. six posts 40) are identical. Thepost 40 includes a shaft portion 41 and a head portion 42. The headportion 42 has an inclined surface 43, angled at 60° with respect to thelongitudinal axis in this embodiment (i.e. 30° with respect to a planeperpendicular to the longitudinal axis). The shaft portion 41 includesan end portion 44 opposite the head portion 42, having a reduceddiameter for engaging the back plate 50. The head portion 42 has alarger cross-sectional dimension than the shaft portion 41 in a planeperpendicular to the longitudinal axis. The head portion 42 has sidesurfaces 47 that are adjacent to the side surfaces of an adjacent postwhen assembled to form the drive unit 4. In order to avoid ashort-circuit of the magnetic flux between the posts 40, a small air gapor other type of insulation is provided between the head portions 42.Further to avoiding a short-circuit, it may be advantageous to providean insulation material between the head portions 42 of the posts 40 thatkeeps the magnetic field within each of the posts 40. In other words,the head portions 42 may be separated by a magnetically insulatingmaterial. For instance, magnets, e.g. plates of a magnetic material, canbe arranged between the head portions 42 to separate the head portions42 and the respective magnetic fields from each other. Radially innersurfaces 48 of the post head portions 42 form a central opening 54. Itwill be appreciated that the transition surface between the surfaces 43and 48 does not need to be rounded.

Different views of another embodiment of a post 40 are shown in FIG. 4 ,which corresponds to the previous embodiment except for slight changesin the shape of the shaft portion 41 and the head portion 42. FIG. 4 ashows a cross-sectional view along the line A-A illustrated in FIG. 4 d, which shows a top view (i.e. towards the head portion 42) of the post40. FIG. 4 b shows a perspective view of the post 40, while FIG. 4 cshows a bottom view (i.e. a view towards the end portion 44 of the shaftportion 41). The post 40 may have an overall length of about 9 to 10 mm,wherein the head portion 42 may have a length of about 2 mm. In thisembodiment, the head portion 42 has a surface 43 which is inclined at anangle of 45° with respect to the axis of rotation or longitudinal axis.Accordingly, the angle 45 between the surface 43 and a ledge 49 shown inFIG. 4 a is 135°. The ledge 49 may serve as a stop when the posts 40 areassembled in a housing. Furthermore, a shoulder 46 is formed by the headportion 42, which may serve as a stop for a coil winding. As describedin connection with FIG. 3 , the head portion 42 comprises side surfaces47 and a radial inner surface 48.

FIG. 5 illustrates an assembly including six posts 40, described inconnection with FIG. 3 . All posts 40 are formed identically, such thateach head portion 42 forms a 60° segment of a circle, that is to say, a“pie slice” of 60°. It will be appreciated that the assembly may includefewer or more posts, such as two, three, four or five or more than six,where the angle depends on the number of posts, e.g. four posts thateach form a 90° segment or eight posts that each form a 45° segment. Asalready mentioned above, the number of posts 40 is preferably even,where diametrically opposed posts 40 may form a pair, e.g. with respectto control of the magnetic field, i.e. each pair of posts may becontrolled as a unit to activate the posts of each respective pairsimultaneously. The head portions 42 form a cone having a conicalsurface formed by the inclined surfaces 43. This can be seen moreclearly in FIG. 6 . In FIG. 6 , the reduced-diameter end portions 44 ofthe shaft portions 41 are mounted in the back plate 50.

In FIG. 7 the same arrangement is illustrated including coil windings 47about the posts 40. The coil windings 47 do not extend radially beyondthe head portions 42, thereby providing for a compact outer dimension.It will be appreciated that preferably the maximum cross-sectional areadefined by the head portions 42 is used for the coil windings 47 tooptimize usage of the available space and to minimize air gaps that actas an insulator and affect the magnetic flux. Suitable materials for thecoil windings are e.g. copper or silver. Further, the diameter of theshaft portions 41 of the posts 40 is chosen so as to optimize the numberof windings of the coil windings 47. FIG. 8 shows a housing 60 which isto be mounted over the post arrangement. The housing 60 conforms to theshape of the post arrangement and comprises a substantially cylindricalportion 62 and a conical end portion 61. The conical end portion 61 istapered at the same angle as the conical surface formed by the inclinedsurfaces 43 of the posts' head portions 42, that is to say, the anglepreferably is between about 30° to 60°, preferably 30° or 45°, withrespect to a plane perpendicular to the longitudinal axis. The housing60 is closed by the back plate 50 at an open end 63 opposite the conicalend portion 61. The conical end portion 61 has a central opening 64 thatis aligned with the central opening 54 formed by the posts 40 and acentral opening 53 in the back plate 50.

The back plate 50 is illustrated in more detail in different views inFIG. 9 (top view in FIG. 9 a , cross-sectional view along line A-A inFIG. 9 b , and cross-sectional view along line B-B in FIG. 9 c ). Theback plate 50 has apertures 51 for receiving the reduced-diameter endportions 44 of the shaft portions 41 of the posts 40. Preferably, thenumber of apertures 51 in the back plate 50 corresponds to the number ofposts 40 of the drive unit 4. In the embodiment shown, six apertures 51are disposed at a regular distance of 60° about the axis of rotation 10,with each of the apertures 51 being at the same distance from the axisof rotation 10. The apertures 51 are shown as extending completelythrough the back plate 50 in the cross-sectional view of FIG. 9 c .However, the apertures 51 may alternatively extend into the back plate50 only up to a certain depth rather than completely through the backplate 50. A central opening 53 is formed for receiving the bearing pin15, as described above. The back plate 50 is made of a magneticmaterial, preferably cobalt steel, to close the magnetic flux path. Thediameter of the back plate 50 may be about 5 to 7 mm. Furthermore,notches 52 are provided at the periphery of the back plate 50 forreceiving wires 56 to connect the coil windings 47 to a control unit 55,such as a printed circuit board (PCB) at the back of the back plate 50,as shown schematically by dashed lines in FIG. 9 b.

Referring to FIG. 10 , the magnet 32 of the impeller 3 (see FIG. 2 ) isshown in a top view (FIG. 10 a ), a cross-sectional view (FIG. 10 b )and a perspective view (FIG. 10 c ). In this embodiment, six magnets 32are provided that are arranged uniformly about the axis of rotation 10,with the orientation of the respective magnetic field alternating. Feweror more magnets, such as four, eight, ten or twelve magnets, may beprovided. The magnets 32 form a recess 35 having a surface 33. Therecess 35 corresponds in size and shape to the conical surface formed bythe surfaces 43 of the head portions 42 of the posts 40, as shown bestin FIG. 6 , taking into account the housing 60 that surrounds the driveunit 4, in particular the conical end portion 61 (FIG. 8 ). It will beappreciated that this includes that the distance between the impeller 3and the drive unit 4 may not be constant but may increase towards theaxis of rotation 10 as explained above. The recess 35 in this embodimenthas a conical shape with an angle 34 of 45° with respect to the axis ofrotation 10 or longitudinal axis. Other angles, such as 60°, arepossible, depending on the shape of the drive unit 4, in particular theend surface formed by the head portions 42 of the posts 40. Furthermore,the magnets 32 form a central opening 36 for receiving the bearing pin15, as shown in FIG. 2 . The central opening 36 is aligned to thecentral opening 54 of the drive unit 4. As shown in FIG. 10 b , themagnetic flux of the magnets 32 is closed by the yoke 37. The yoke 37may have any suitable shape depending on the shape of the impeller 3,such as conical as shown in FIG. 2 or disc-shaped as indicated in FIG.10 b . Optionally, an encapsulation 38 is provided that encloses themagnets 32 and, if applicable, the yoke 37 to protect the magnets 32 andyoke 37 against corrosion.

In FIG. 11 is illustrated another embodiment of a drive unit which issubstantially similar to the aforementioned embodiments. The arrangementincludes six posts 40′ having a respective coil winding 47 on theirshaft portions 41′. As in the previous embodiments, there may be feweror more posts 40′. The posts 40′ are preferably attached to a back plate(not shown) as in the previous embodiments. The posts 40 each include ahead portion 42′, which has a different shape from the above describedhead portions 42. Although the angle may be the same as described above,the inclined surfaces 43′ face radially inwards rather than radiallyoutwards. That is to say, the head portions 42′ form a substantiallyconical recess. It will be appreciated that the magnet of the impellerwill be shaped accordingly, i.e. the magnet will have a correspondingconical shape rather than a conical recess as in the previousembodiments. As in the previous embodiments, the drive unit has acentral opening 54′. The posts 40′ in the embodiment of FIG. 11 areseparated by gaps 57′ that prevent a bypass or short-circuit between theposts 40′, whereas the head portions 42 of the posts 40 in the previousembodiments are shown to be directly adjacent to each other or separatedonly by small gaps. It will be appreciated, however, that ashort-circuit between the posts is to be avoided in all embodiments.

With reference to FIG. 12 , another embodiment of a blood pump 1 isshown, which is similar to that of FIGS. 1 and 2 . In contrast to theabove embodiment, the blood pump 1 of FIG. 12 has an additional radialhydrodynamic bearing. A circumferential portion 28 of the pump casing 2or sleeve is provided to form a gap 27 between the impeller 3 and thecircumferential portion 28. In addition to the blood flow outlet 22 afurther blood flow outlet 29 allows blood to flow through the gap 27 andout of the pump casing 2. The size of the gap 27 is chosen so as to forma radial hydrodynamic bearing.

FIGS. 13 a and 13 b schematically illustrate the magnets 32 of theimpeller and the magnets 32 arranged with respect to the drive unit 4.In this embodiment, four magnets 32 are provided that are separated byrespective gaps 66. The gaps 66, which may be formed as channels betweenthe surfaces 33 of the magnets 32, extend in a radial direction from thecentral opening 36 towards the outer perimeter of the magnets 32. Aswill be described in more detail below with reference to FIGS. 15 a and15 b , the reduction of the size of the magnets 32 does not cause a lossof efficiency of the magnetic coupling. FIG. 13 b illustrates therelative arrangement of the magnets 32 and the drive unit 4, where a gap65 is provided between the drive unit 4 (i.e. the stator) and themagnets 32 of the impeller (i.e. the rotor). The channels or gaps 66improve washing of the gap 65 since they cause a centrifugal pump effectfor the blood.

With reference to FIGS. 14 a and 14 b , the principle of the magneticcoupling between the rotor, in particular the magnets 32, and thestator, i.e. the drive unit 4, is schematically illustrated. In FIG. 14a , the magnets 32 are not or substantially not separated by a gap. Someexemplary magnetic field lines from north N to south S are illustrated.Due to the gap 65 between the drive unit 4 and the magnets 32 theinnermost magnetic field lines do not interact with the drive unit 4.That is to say, this part of the magnetic field does not contribute tothe drive of the impeller. Thus, no efficiency of the magnetic couplingwill be lost if a gap 66 is provided between the magnets 32. In FIG. 14b , the same amount of magnetic field lines reaches the drive unit 4 asin FIG. 14 a . As a skilled person knowing the orientation of magneticfield lines is able to calculate, the size of the gap 66 is directlydependent on the size of the gap 65.

With reference to FIG. 15 , another embodiment of a drive arrangementfor a blood pump is shown. The drive unit 4, including the posts 40 withcoil windings 47, is substantially the same as described above. Likereference numerals refer to like parts. As in the previous embodiments,the drive unit 4 includes a back plate 50. However, the design of theimpeller is different. In FIG. 15 only the magnets 32 and the yoke 37 ofthe impeller are shown. The impeller has an increased diameter, inparticular a larger diameter than the drive unit 4, and an axialextension 39 such that the extension 39 extends circumferentially aboutthe drive unit 4, in particular in the area of the head portions 42 ofthe posts 40. This arrangement allows for improved magnetic coupling, aswill be explained in the following.

As indicated by some exemplary schematic magnetic field lines, theextension 39 causes the magnetic coupling between the magnets 32 and thedrive unit 4 to occur not only in the region of the inclined surfaces 43but also in the region of the outer side surfaces of the head portions42 of the posts 40. In this region, the magnetic field lines extend in asubstantially radial direction between the blood pump's rotor and statorand a high torque can be created to drive the impeller. As alsoillustrated in FIG. 15 , as in all other embodiments, the magnetic fieldlines form a closed loop that extends through the posts 40, includingthe head portions 42 and the shaft portions 41, through the magnets 32and through both end plates or yokes 50 and 37.

With reference to FIG. 16 , the operating mode of the drive unit isschematically illustrated in an example having six posts 40 a, 40 b, 40c, 40 d, 40 e and 40 f In order to create a rotating magnetic field, theposts are controlled sequentially. The posts are controlled in pairs toestablish a balanced rotation of the impeller, in which diametricallyopposing posts 40 a and 40 d, 40 b and 40 e, and 40 c and 40 frespectively form pairs. The magnetic density can be increased byactivating four of the six posts at the same time. FIG. 13 illustrates asequence with three steps, in which the activated posts are marked. Inthe first step, the posts 40 a, 40 c, 40 d and 40 f are activated, i.e.a current is supplied to the respective coil winding to create amagnetic field. In the second step, the posts 40 a, 40 b, 40 d and 40 eare activated, while in the third step, the posts 40 b, 40 c, 40 e and40 f are activated. This sequence is repeated to create the rotatingmagnetic field.

FIGS. 17 to 21 illustrate embodiments which are substantially similar tothe aforementioned embodiments with the main difference that the partsof the drive unit are not formed as a solid body but are slotted orotherwise formed by a discontinuous material as will be described inmore detail below. It will be appreciated that the features andfunctions described above with respect to FIGS. 1 to 16 are likewiseapplicable for the following embodiment. Thus, like reference numeralsenhanced by 100 refer to like parts of the blood pump, drive unit andother parts of the blood pump. Vice versa it will be appreciated thatthe aforementioned embodiments may be provided with slotted componentsor discontinuous soft magnetic material as will be described below.

FIG. 17 shows a perspective view of a drive unit 104 without coilwindings and magnets similar to the view shown in FIG. 6 . The driveunit 104 comprises six posts 140 each having a shaft portion 141 and ahead portion 142 as explained above with respect to the previousembodiment. The posts 140 are attached to a back plate 150 similar tothe previous embodiment. The head portions 142 have a flat top surfacethat extends in a plane perpendicular to the axis of rotation, i.e. thelongitudinal axis of the drive unit 104.

In contrast to the above described embodiments, components of the driveunit 104, more specifically the shaft portions 141 of the posts 140 aswell as the back plate 150 comprise a soft magnetic material that isdiscontinuous in respective cross-sections transverse to the directionof the magnetic flux (see FIG. 15 for a schematic illustration of themagnetic flux). In particular, the shaft portions 141 and the back plate150 are slotted, i.e. they are formed of a stack of sheets of softmagnetic material that are electrically insulated from each other. Thesheets may have a thickness from about 50 μm to about 350 μm, e.g. 100μm. The insulating layers may have a thickness of about 1 μm to about 50μm. Optionally, the head portions 142 may be slotted, too, as will bedescribed in more detail below.

The shaft portions 141 are formed of sheets 171 insulated from eachother by insulating layers 172, and the back plate is formed of sheets175 insulated from each other by insulating layers 176. The sheets 171of the shaft portions extend parallel to the axis of rotation, as can beseen also in FIGS. 19 a to 19 d , so as to provide a discontinuouscross-section transverse to the axis of rotation. The back plate 150 isformed of sheets 175 that extend in planes perpendicular to the axis ofrotation so as to provide a discontinuous cross-section parallel to theaxis of rotation. It will be appreciated that the back plate 150 may beformed of a solid material, i.e. may not be slotted. The slottedconstruction reduces eddy currents and, thus, heat generation and energyloss, i.e. energy consumption.

FIG. 18 shows the back plate 150 in more detail. Similar to the backplate shown in FIG. 9 , the back plate 150 has a central opening 153 andnotches 152. As explained above, the back plate 150 is made of aplurality of stacked sheets 175 insulated from each other by insulatinglayers 176. FIG. 19 a shows one of the posts 140 in more detail, havingthe shaft portion 141 and the head portion 142 with a top surface 143.The top surface is not inclined. Ends 144 of the posts 140 fit into theopenings 151 in the back plate 150. In contrast to the embodimentdescribed above, the ends 144 do not have shoulder. The head portion 142extends laterally beyond the shaft portion 141 such that coil windingsdo not extend beyond the head portion 142 as explained above. FIG. 19 bshows an embodiment of a post 140′ with a shaft portion 141′ and a headportion 142′ in which the top surface 143′ is inclined as explained indetail for the previous embodiment.

In one embodiment, as shown in FIG. 19 c , the head portions 142 of theposts 140 may be formed of a discontinuous soft magnetic material, too.More specifically, the head portion 142 of each of the posts 140 maycomprises a soft magnetic material which is discontinuous incross-section perpendicular to the longitudinal axis of the respectivepost 40, similar to the shaft portions 141 of the posts 140. The headportions 142 may be formed of sheets 173 insulated from each other byinsulating layers 174. Due to the small height of the flat head portions142, the sheets 173 may also be referred to as “rods”. As shown in FIG.19 d , the inclined head 142′ may also be formed of a discontinuous softmagnet material, in particular formed of sheets 173′ insulated from eachother by insulating layers 174′. All characteristics of thediscontinuous soft magnetic material described above for the shaftportions 141, 141′ may apply for the respective head portions 142, 142′.

In FIG. 20 a , the magnets 132 are illustrated adjacent the headportions 142. Since the top surfaces of the head portions 142 are notinclined, the magnets 132 form a substantially cylindrical component.FIG. 20 b shows an alternative embodiment in which the magnets 132′ areseparated by gaps 133′. As explained above, it has been found that theefficiency of the magnetic coupling does not decrease if the magnets132′ are separated by gaps 133′, in particular radially extending gaps,because of the characteristics of the magnetic field and the gap betweenthe drive unit 104 and the impeller.

FIGS. 21 a to 21 j illustrate various embodiments of posts seen incross-section along the line I-I in FIG. 19 a . FIGS. 21 a to 21 d showembodiments in which the shaft portion 141 of the posts is slotted, i.e.is formed of a plurality of sheets 171 insulated from each other byinsulating layers 172. The insulating layers 172 can comprise adhesive,lacquer, baking enamel or the like. FIGS. 21 a and 21 b show embodimentsin which the thickness of the sheets 171 is uniform. The thickness maybe in the range from about 25 μm to about 250 μm. The sheets 171 shownin FIG. 21 a have a greater thickness than the sheets 171 shown in FIG.21 b . The sheets in FIG. 21 c have varying thicknesses, with thecentral sheet having the greatest thickness and the outermost sheetshaving the smallest thickness. This may be advantageous because eddycurrents in the side regions of the shaft portions are more critical andcan be reduced by the thin sheets. Eddy currents in the central area areless critical, and the relatively thick central sheet may help inimproving the magnetic flux. The orientation of the sheets 171 may bedifferent as exemplarily shown in FIG. 21 d as long as the soft magneticmaterial in the shown cross-section, i.e. the soft magnetic material incross-section transverse to the direction of the magnetic flux, isdiscontinuous or interrupted.

FIGS. 21 e and 21 f show embodiments in which the shaft portions 141 areformed by a bundle of wires 181 which are insulated from each other byan insulating material 182. The insulating material 182 may be presentas a coating of each of the wires 181 or may be a matrix in which thewires 181 are embedded. In the embodiment of FIG. 21 e all wires havethe same diameter, whereas in the embodiment of FIG. 21 f a central wirehas a largest diameter and outer wires have smaller diameters, similarto the embodiment shown in FIG. 21 c having sheets with varyingthicknesses. As shown in FIG. 21 g , wires 181 of different diametersmay be mixed, which may increase the total cross-sectional area of softmagnetic material compared to embodiments in which all wires have thesame diameter. Still alternatively, in order to further minimizeinsulating layers 184 between the wires 183, the wires 183 may have apolygonal cross-sectional area, such as rectangular, square etc.

Alternatively, the discontinuous cross-section of the shaft portions 141may be created by metal particles 185 embedded in a polymer matrix 186as shown in FIG. 21 i , or by steel wool or other porous structuresimpregnated with an insulating matrix. A porous and, thus, discontinuousstructure of soft magnetic material may also be produced by a sinteringprocess or high-pressure molding process, in which an insulating matrixmay be omitted because insulating layers are formed automatically byoxidation of the soft magnetic material by exposure to air. Stillalternatively, the shaft portion 141 may be formed of a rolled-up sheet187 of a soft magnetic material in which the layers of the rolled-upsheet 187 are separated by insulating layers 188 as shown in FIG. 21 j .This also provides a discontinuous cross-section in the sense of thepresent invention which reduces eddy currents in the shaft portions 141of the posts 140.

1-15. (canceled)
 16. An intravascular blood pump for percutaneousinsertion into a patient's blood vessel, the intravascular blood pumpcomprising: a pump casing having a blood flow inlet and a blood flowoutlet; an impeller arranged in the pump casing so as to be rotatableabout an axis of rotation, the impeller having at least one magnet andblades for conveying blood from the blood flow inlet to the blood flowoutlet; and a drive unit magnetically coupled to the at least one magnetof the impeller for rotating the impeller; the drive unit comprising aplurality of posts, with each post including a head portion and a shaftportion, and a plurality of coil windings, the plurality of postsarranged about the axis of rotation, wherein the plurality of coilwindings are disposed about the shaft portion of each correspondingpost, the plurality of coil windings being sequentially controllable soas to create a rotating magnetic field.
 17. The blood pump of claim 16,wherein the at least one magnet is a multiple-piece magnet.
 18. Theblood pump of claim 16, wherein the at least one magnet is disposed atan end of the impeller facing the drive unit.
 19. The blood pump ofclaim 16, wherein the at least one magnet has a cylindrical shape. 20.The blood pump of claim 16, wherein the at least one magnet has a recessthat corresponds in size and shape to a surface formed by the headportions of the plurality of posts.
 21. The blood pump of claim 16,wherein the at least one magnet has a central opening for receiving abearing pin.
 22. The blood pump of claim 16, wherein the shaft portionof each of the plurality of posts comprises a soft magnetic materialwhich is discontinuous in cross-section transverse to a longitudinalaxis of the respective post.
 23. The blood pump of claim 22, wherein thesoft magnetic material is provided as a first plurality of sheets of asoft magnetic material.
 24. The blood pump of claim 23, wherein each ofthe first plurality of sheets is electrically insulated from each other.25. The blood pump of claim 24, wherein each of the first plurality ofsheets is electrically insulated from each other by insulating layers,each insulating layer having a thickness of about 1 μm to about 50 μm.26. The blood pump of claim 23, wherein each of the first plurality ofsheets extends parallel to the longitudinal axis of the respective post.27. The blood pump of claim 23, wherein each of the first plurality ofsheets has a thickness of about 25 μm to about 350 μm.
 28. The bloodpump of claim 22, wherein the head portion of each of the plurality ofposts comprises the soft magnetic material.
 29. The blood pump of claim28, wherein the soft magnetic material in the head portion is providedas a second plurality of sheets, and wherein the second plurality ofsheets extend in the same direction as the first plurality of sheets inthe shaft portions.
 30. The blood pump of claim 16, wherein each of thehead portions comprises a top surface, and wherein each of the headportions of the plurality posts extends in a plane perpendicular to theaxis of rotation.
 31. The blood pump of claim 30, wherein each of thetop surfaces of each of the head portions, as seen in a top view in anaxial direction, is aligned with the respective shaft portion in theaxial direction.
 32. The blood pump of claim 22, wherein the softmagnetic material is provided as a plurality of wires of the softmagnetic material, which are electrically insulated from each other. 33.The blood pump of claim 16, wherein the drive unit further comprises aback plate, wherein each of the shaft portions of the plurality of postsfurther comprises an end, and wherein the back plate engages each of theends of the shaft portions of the posts opposite the head portions. 34.The blood pump of claim 33, wherein the back plate comprises a softmagnetic material which is discontinuous in cross-section parallel to alongitudinal axis of the respective post.
 35. The blood pump of claim33, wherein the soft magnetic material is provided as a plurality ofsheets of the soft magnetic material.